Total Synthesis of (-)-Arborisidine

An asymmetric total synthesis of cage-like indole alkaloid arborisidine is presented. The new synthetic strategy features a catalytic parallel kinetic resolution based on ambident nucleophilicity (C3/N) of indole to set the absolute configurations of the two quaternary chiral centers, and a 5-exo-trig radical cyclization to form the bridged nitrogen-containing five-membered ring.

Rhodium-catalyzed asymmetric hydrogenation of β-cyanocinnamic esters with the assistance of a single hydrogen bond in a precise position

The first asymmetric hydrogenation of β-cyanoacrylate esters has been developed to furnish chiral β-cyano esters with excellent yields and excellent enantioselectivities. Notably, the catalyst with a single H-bond donor in a precise position performed better than that with double H-bond donors.

With the assistance of hydrogen bonds, the first asymmetric hydrogenation of β-cyanocinnamic esters is developed, affording chiral β-cyano esters with excellent enantioselectivities (up to 99% ee). This novel methodology provides an efficient and concise synthetic route to chiral GABA-derivatives such as (S)-Pregabalin, (R)-Phenibut, (R)-Baclofen. Interestingly, in this system, the catalyst with a single H-bond donor performs better than that with double H-bond donors, which is a novel discovery in the metalorganocatalysis area.

A mild and efficient approach to enantioenriched α-hydroxyethyl α,β-unsaturated δ-lactams

A straightforward approach toward enantioenriched α-substituted α,β-unsaturated δ-lactams is described. Although a considerable number of approches toward α,β-unsaturated δ-lactams have been reported, there are relatively few examples of enantioenriched α,δ-disubstituted α,β-unsaturated δ-lactams formation. The δ-stereocenter was formed by addition of allylmagnesium bromide to an N-tert-butylsulfinyl imine. The α,β-unsaturated δ-lactam was furnished by ring-closing metathesis. Although Baylis-Hillman chemistry failed on this cyclic compound, introduction of the hydroxyethyl group prior to ring-closing metathesis was successful. A Baylis-Hillman reaction was used to introduce the substituent at the α-position of the α,β-unsaturated lactam.

Synthesis of γ-lactams and γ-lactones via intramolecular Pd-catalyzed allylic alkylations

CONSPECTUS: Lactones and lactams are a well-known class of natural products and can be used as building blocks in organic synthesis. In addition, they can be found in many natural sources and synthetic drugs and have a broad range of biological or odorant properties. Chemists can create these useful compounds through palladium catalysis, which is a highly efficient tool for organic synthesis and is conveniently functional group tolerant. In this Account, we describe our work over the past 15 years in intramolecular Pd-catalyzed allylations where we have tethered the nucleophile and the electrophile by either an amide or an ester moiety, to produce γ-lactams and γ-lactones. We discuss in detail how the nature of the heteroatom tether influences the regioselectivity of the reaction. For example, a ketone [-C(O)CH2-] tether leads to mixtures of 5-exo and 7-endo cyclization products, while ester or amide [-C(O)X-] tethers afford sole 5-exo products. However, in the case of X = O, we were required to overcome two issues in the synthesis of γ-lactones. First of all, the tethering ester function can compete with the allylic leaving group in the oxidative addition to the Pd(0) center. Second, in this case, the proportion of the conformers that have a suitable geometry for cyclization is very low. When we insert a juxtaposed silyl group on the allyl fragment, the molecule can undergo oxidative addition and functionalization of the lactone via Hiyama cross-coupling. We also performed DFT calculations on these systems, which allowed us to better understand the behavior of [-C(O)X-] and [-C(O)CH2-] tethers. Computations also let us rationalize the different reactivities that we observed as a function of the geometry (Z or E) of the starting substrates. In addition, we were able to synthesize natural products or analogs (α-kainic acid, isoretronecanol, and picropodophyllin). We could turn these allylation reactions into asymmetric transformations and incorporate them into domino sequences. Thus, an allylation/Mizoroki-Heck sequence allowed us to straightforwardly access an aza-analog of picropodophyllin, as well as reach the lysergic acid backbone. Finally, we found that through carbopalladation of allenes, we could efficiently synthesize the key η(3)-allylpalladium intermediates that were then ready for allylation reactions.

Silver-free two-component approach in gold catalysis: activation of [LAuCl] complexes with derivatives of copper, zinc, indium, bismuth, and other Lewis acids

Complexes of type [LAuCl] (L = phosphine, phosphite, NHC and others) are widely employed in homogeneous catalysis, however, they are usually inactive as such and must be used jointly with a halide scavenger. To date, this role has mostly been entrusted to silver salts (AgSbF6 , AgPF6, AgBF4, AgOTf, etc.). However, silver salts can be the source of deactivation processes or side reactions, so it is sometimes advisable to use silver-free cationic gold complexes, which can be difficult to synthesize and to handle compared with the more robust chloride. We show in this study that various Lewis acids of the transition and main group metal families are expedient substitutes to silver salts. We have tested Cu(I), Cu(II), Zn(II), In(III), Si(IV), Bi(III), and other salts in a variety of typical Au(I)-catalyzed transformations, and the results have revealed that [LAuCl] can form active species in their presence.

Synthesis of 1,4-benzodiazepinones and 1,4-benzoxazepinones via palladium-catalyzed amino and oxyacetoxylation

Palladium-catalyzed amino and oxyacetoxylation have been developed to furnish 1,4-benzodiazepinones and 1,4-benzoxazepinones through the diheterofunctionalization of alkenes.

Mechanistic investigation of the iridium-catalysed alkylation of amines with alcohols

The [Cp*IrCl(2)](2)-catalysed alkylation of amines with alcohols was investigated using a combination of experimental and theoretical methods. A Hammett study involving a series of para-substituted benzyl alcohols resulted in a line with a negative slope. This clearly documents that a positive charge is built up in the transition state, which in combination with the measurement of a significant kinetic isotope effect determines hydride abstraction as being the selectivity-determining step under these conditions. A complementary Hammett study using para-substituted anilines was also carried out. Again, a line with a negative slope was obtained suggesting that nucleophilic attack on the aldehyde is selectivity-determining. A computational investigation of the entire catalytic cycle with full-sized ligands and substrates was performed using density functional theory. The results suggest a catalytic cycle where the intermediate aldehyde stays coordinated to the iridium catalyst and reacts with the amine to give a hemiaminal which is also bound to the catalyst. Dehydration to the imine and reduction to the product amine also takes place without breaking the coordination to the catalyst. The fact that the entire catalytic cycle takes place with all the intermediates bound to the catalyst is important for the further development of this synthetic transformation.